drm/i915: Rename i915->gt to i915->gt0

In preparation of the multitile support, highlight the root GT by
calling it gt0 inside the drm i915 private data.
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211214193346.21231-11-andi.shyti@linux.intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1189,7 +1189,7 @@ struct drm_i915_private {
 	struct i915_perf perf;
 
 	/* Abstract the submission mechanism (legacy ringbuffer or execlists) away */
-	struct intel_gt gt;
+	struct intel_gt gt0;
 
 	struct {
 		struct i915_gem_contexts {
@@ -1270,7 +1270,7 @@ static inline struct drm_i915_private *pdev_to_i915(struct pci_dev *pdev)
 
 static inline struct intel_gt *to_gt(struct drm_i915_private *i915)
 {
-	return &i915->gt;
+	return &i915->gt0;
 }
 
 /* Simple iterator over all initialised engines */